Home > Articles > Cisco Certification > CCIE > CCIE Self-Study: Security Protocols

CCIE Self-Study: Security Protocols

  • Sample Chapter is provided courtesy of Cisco Press.
  • Date: Oct 28, 2005.

Chapter Description

This chapter covers some of today's most widely used technologies that enable network administrators to ensure that sensitive data is secure from unauthorized sources. Standards such as IP Security (IPSec) and encryption standards are covered, as are all the fundamental foundation topics you need to understand to master the topics covered in the CCIE Security written exam.

Remote Authentication Dial-In User Service

RADIUS is a client/server-based system that secures a Cisco network against intruders. Implemented in Cisco IOS, RADIUS sends authentication requests to a RADIUS server. RADIUS was created by Livingston Enterprises and is now defined in RFCs 2865/2866 (RFCs 2138/2139 are now obsolete).

A RADIUS server is a device that has the RADIUS daemon or application installed. RADIUS must be used with AAA to enable the authentication, authorization, and accounting of remote users when using Cisco IOS routers.

When a RADIUS server authenticates a user, the following events occur:

  1. The user is prompted for and enters a username and password.

  2. The username and encrypted password are sent over the network to the RADIUS server. These events are sent via the packet format known as Access-Request.

  3. The user receives one of the following responses from the RADIUS server:

  • ACCESS-ACCEPT— The user is authenticated.
  • ACCESS-REJECT— The user is not authenticated and is prompted to re-enter the username and password, or access is denied. The RADIUS server sends this response when the user enters an invalid username/password pairing.
  • ACCESS-CHALLENGE— A challenge is issued by the RADIUS server. The challenge collects additional data from the user.
  • CHANGE PASSWORD— The RADIUS server issues a request asking the user to select a new password.

An ACCESS-ACCEPT or ACCESS-REJECT response may contain additional information for services that the user can access, including Telnet, rlogin, or local-area transport (LAT) connections, and PPP, Serial Line Internet Protocol (SLIP), or EXEC services.

RADIUS is commonly used when PPP is used. Figure 4-2 displays a typical PPP connection request to a RADIUS server.

04fig02.gif

Figure 4-2 RADIUS Sequence Example

The RADIUS server accepts or rejects a username and password pair. In some instances, a user might be asked to enter more information (this is called a challenge response). For example, if a user's password has expired, a RADIUS server prompts the user for a new password.

Transactions between the client (end user) and the RADIUS server are authenticated through a shared secret. The username is sent as clear text. RADIUS supports both Password Authentication Protocol (PAP) and Challenge Handshake Authentication Protocol (CHAP). PAP and CHAP are security protocols that allow users to gain access to remote devices with PPP. A RADIUS server will never send the user's password over the network in any circumstance. If the username/password pairing is entered incorrectly, the RADIUS server sends an ACCESS-REJECT response. The end user must re-enter the pairings or the connection will be rejected. Note that PAP sends the end user's password in the clear to the NAS, but from the NAS to the RADIUS server (the NAS and the RADIUS communicate using the shared secret), the end user's password is encrypted.

RADIUS supports a number of predefined attributes that can be exchanged between client and server, such as the client's IP address. RADIUS attributes carry specific details about authentication.

RFC 2138 defines a number of attributes. The following list provides details for the most common attributes:

  • Attribute type 1— Username (defines usernames, such as numeric, simple ASCII characters, or a Simple Mail Transfer Protocol [SMTP] address).
  • Attribute type 2— User Password (defines the password, which is encrypted using Message Digest 5 [MD5]).
  • Attribute type 3— CHAP Password (used only in access-request packets).
  • Attribute type 4— NAS IP Address (defines the NAS's IP address; used only in access-request packets).
  • Attribute type 5— NAS Port (this is not the User Datagram Protocol [UDP] port number; it indicates the NAS's physical port number, ranging from 0 to 65,535).
  • Attribute type 6— Service-Type of service requested or type of service to be provided. Now supported in Cisco IOS. See (requires CCO login) http://www.cisco.com/en/US/partner/products/sw/iosswrel/ps1839/products_feature_guide09186a0080110bed.html#1024276.
  • Attribute type 7— Framed-Protocol defines required framing; for example, PPP is defined when this attribute is set to 1 and SLIP is set to 2.
  • Attribute type 8— Framed-IP-Address defines the IP address to be used by the remote user.
  • Attribute type 9— Framed-IP-Netmask defines the subnet mask to be used by the remote user.
  • Attribute type 10— Framed-Routing.
  • Attribute type 13 —Framed-Compression.
  • Attribute type 19— Callback-Number.
  • Attribute type 26— Vendor-Specific. Cisco (vendor-ID 9) uses one defined option: vendor type 1 named cisco-avpair; this attribute transmits TACACS+ A/V pairs.
  • Attribute type 61— NAS-Port-Type

Table 4-2 summarizes the RADIUS protocol's main features.

Table 4-2. Summary of RADIUS Protocol Features

Feature

Description

UDP

Packets sent between the client and server are UDP, primarily because TCP's overhead does not allow for significant advantages. Typically, the user can wait for a username/password prompt.

UDP destination port

1812 and 1813. Defined in RFC 2865, which supersedes RFC 2138. Early deployments RADIUS used UDP ports 1645 and 1646.

Attributes

Attributes are used to exchange information between the NAS and client.

Model

Client/server-based model in which packets are exchanged in a unidirectional manner.

Encryption method

The password is encrypted using MD5; the username is not encrypted. RADIUS encrypts only the password in the access-request packet, sent from the client to the server. The remainder of the packet is transmitted in clear text. A third party could capture other information, such as the username, authorized services, and accounting information.

Multiprotocol support

Does not support protocols such as AppleTalk, NetBIOS, or IPX. IP is the only protocol supported.

Now, examine the RADIUS configuration tasks required on a Cisco router.

IETF Attribute 26 (Vendor-Specific) encapsulates vendor-specific attributes, thereby allowing vendors to support their own extended attributes. Attribute 26 contains the following three elements:

  • Type
  • Length
  • String (also known as data)

RADIUS Configuration Task List

A RADIUS server is usually software that runs on a variety of platforms, including Microsoft Windows 2000 Server and various UNIX hosts. RADIUS can authenticate router users and even validate IP routes.

To configure RADIUS on your Cisco router or NAS, perform the following tasks:

Step 1.

Enable AAA with the aaa new-model global configuration command. AAA must be configured if you plan to use RADIUS.

Step 2.

Use the aaa authentication global configuration command to define method lists for RADIUS authentication.

Step 3.

Use line and interface commands to enable the defined method lists to be used.

Step 4.

Define the RADIUS server and secret key with the following IOS commands:


         radius-server 
         ip-address

         radius-server key secret-key

      

Examples are the best method to show the enormous IOS command set that is available for use when configuring RADIUS support with AAA.

Example 4-3 configures a Cisco IOS router with AAA and RADIUS support.

Example 4-3. AAA and RADIUS IOS Configuration


   aaa new-model
aaa authentication login use-radius group radius local
aaa authentication ppp user-radius if-needed group radius
aaa authorization exec default group radius
aaa authorization network default group radius
radius-server 3.3.3.3
radius-server key ccie2005
! Ensure you apply the named access list on the VTY line
line vty 0 4
aaa authentication login

The command lines in this RADIUS authentication and authorization configuration are defined as follows:

  • The aaa authentication login use-radius group radius local command configures the router to use RADIUS for authentication at the login prompt. If RADIUS returns an error, the user is authenticated using the local database. In this example, use-radius is the name of the method list, which specifies RADIUS and then local authentication. If the RADIUS server returns the ACCESS-REJECT response, the user is denied access and the router will not check its local database.
  • The aaa authentication ppp user-radius if-needed group radius command configures the Cisco IOS software to use RADIUS authentication for lines using PPP with CHAP or PAP, if the user is not already authorized. If the EXEC facility has authenticated the user, RADIUS authentication is not performed. In this example, user-radius is the name of the method list defining RADIUS as the if-needed authentication method.
  • The aaa authorization exec default group radius command sets the RADIUS information used for EXEC authorization, autocommands, and access lists.
  • The aaa authorization network default group radius command sets RADIUS for network authorization, address assignment, and access lists.
  • The radius-server commands define the NAS.
  • The radius-server key commands define the shared secret text string between the NAS and the RADIUS server host.

Example 4-4 displays an example in which AAA is enabled on a Cisco IOS router.

Example 4-4. AAA and RADIUS Example


   Hostname R1
username simon password SimonisisAgreatdrummeR
aaa new-model                                                              
aaa authentication ppp dialins group radius local
aaa authorization network default group radius local
aaa accounting network default start-stop group radius
aaa authentication login simon local
aaa authorization exec default local
radius-server host 3.3.3.3
radius-server key CCIEsrock
line vty 0 4
login authentication radius-login

The Example 4-4 line configurations are defined as follows:

  • The radius-server host command defines the RADIUS server host's IP address.
  • The radius-server key command defines the shared secret text string between the NAS and the RADIUS server host.
  • The aaa authentication ppp dialins group radius local command defines the authentication method list, dialins, which specifies that RADIUS authentication and then (if the RADIUS server does not respond) local authentication will be used on serial lines using PPP.
  • The aaa authorization network default group radius local command sets RADIUS for network authorization, address assignment, and access lists.
  • The aaa accounting network default start-stop group radius command tracks PPP usage. This command is used for all network services. It can be PPP, but also SLIP or ARAP.
  • The aaa authentication login simon local command defines the method list, simon, for local authentication.
  • The aaa authentication login simon command applies the simon method list for login authentication.
4. Terminal Access Controller Access Control System Plus | Next Section Previous Section

Cisco Press Promotional Mailings & Special Offers

I would like to receive exclusive offers and hear about products from Cisco Press and its family of brands. I can unsubscribe at any time.

Overview

Pearson Education, Inc., 221 River Street, Hoboken, New Jersey 07030, (Pearson) presents this site to provide information about Cisco Press products and services that can be purchased through this site.

This privacy notice provides an overview of our commitment to privacy and describes how we collect, protect, use and share personal information collected through this site. Please note that other Pearson websites and online products and services have their own separate privacy policies.

Collection and Use of Information

To conduct business and deliver products and services, Pearson collects and uses personal information in several ways in connection with this site, including:

Questions and Inquiries

For inquiries and questions, we collect the inquiry or question, together with name, contact details (email address, phone number and mailing address) and any other additional information voluntarily submitted to us through a Contact Us form or an email. We use this information to address the inquiry and respond to the question.

Online Store

For orders and purchases placed through our online store on this site, we collect order details, name, institution name and address (if applicable), email address, phone number, shipping and billing addresses, credit/debit card information, shipping options and any instructions. We use this information to complete transactions, fulfill orders, communicate with individuals placing orders or visiting the online store, and for related purposes.

Surveys

Pearson may offer opportunities to provide feedback or participate in surveys, including surveys evaluating Pearson products, services or sites. Participation is voluntary. Pearson collects information requested in the survey questions and uses the information to evaluate, support, maintain and improve products, services or sites; develop new products and services; conduct educational research; and for other purposes specified in the survey.

Contests and Drawings

Occasionally, we may sponsor a contest or drawing. Participation is optional. Pearson collects name, contact information and other information specified on the entry form for the contest or drawing to conduct the contest or drawing. Pearson may collect additional personal information from the winners of a contest or drawing in order to award the prize and for tax reporting purposes, as required by law.

Newsletters

If you have elected to receive email newsletters or promotional mailings and special offers but want to unsubscribe, simply email information@ciscopress.com.

Service Announcements

On rare occasions it is necessary to send out a strictly service related announcement. For instance, if our service is temporarily suspended for maintenance we might send users an email. Generally, users may not opt-out of these communications, though they can deactivate their account information. However, these communications are not promotional in nature.

Customer Service

We communicate with users on a regular basis to provide requested services and in regard to issues relating to their account we reply via email or phone in accordance with the users' wishes when a user submits their information through our Contact Us form.

Other Collection and Use of Information

Application and System Logs

Pearson automatically collects log data to help ensure the delivery, availability and security of this site. Log data may include technical information about how a user or visitor connected to this site, such as browser type, type of computer/device, operating system, internet service provider and IP address. We use this information for support purposes and to monitor the health of the site, identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents and appropriately scale computing resources.

Web Analytics

Pearson may use third party web trend analytical services, including Google Analytics, to collect visitor information, such as IP addresses, browser types, referring pages, pages visited and time spent on a particular site. While these analytical services collect and report information on an anonymous basis, they may use cookies to gather web trend information. The information gathered may enable Pearson (but not the third party web trend services) to link information with application and system log data. Pearson uses this information for system administration and to identify problems, improve service, detect unauthorized access and fraudulent activity, prevent and respond to security incidents, appropriately scale computing resources and otherwise support and deliver this site and its services.

Cookies and Related Technologies

This site uses cookies and similar technologies to personalize content, measure traffic patterns, control security, track use and access of information on this site, and provide interest-based messages and advertising. Users can manage and block the use of cookies through their browser. Disabling or blocking certain cookies may limit the functionality of this site.

Do Not Track

This site currently does not respond to Do Not Track signals.

Security

Pearson uses appropriate physical, administrative and technical security measures to protect personal information from unauthorized access, use and disclosure.

Children

This site is not directed to children under the age of 13.

Marketing

Pearson may send or direct marketing communications to users, provided that

  • Pearson will not use personal information collected or processed as a K-12 school service provider for the purpose of directed or targeted advertising.
  • Such marketing is consistent with applicable law and Pearson's legal obligations.
  • Pearson will not knowingly direct or send marketing communications to an individual who has expressed a preference not to receive marketing.
  • Where required by applicable law, express or implied consent to marketing exists and has not been withdrawn.

Pearson may provide personal information to a third party service provider on a restricted basis to provide marketing solely on behalf of Pearson or an affiliate or customer for whom Pearson is a service provider. Marketing preferences may be changed at any time.

Correcting/Updating Personal Information

If a user's personally identifiable information changes (such as your postal address or email address), we provide a way to correct or update that user's personal data provided to us. This can be done on the Account page. If a user no longer desires our service and desires to delete his or her account, please contact us at customer-service@informit.com and we will process the deletion of a user's account.

Choice/Opt-out

Users can always make an informed choice as to whether they should proceed with certain services offered by Cisco Press. If you choose to remove yourself from our mailing list(s) simply visit the following page and uncheck any communication you no longer want to receive: www.ciscopress.com/u.aspx.

Sale of Personal Information

Pearson does not rent or sell personal information in exchange for any payment of money.

While Pearson does not sell personal information, as defined in Nevada law, Nevada residents may email a request for no sale of their personal information to NevadaDesignatedRequest@pearson.com.

Supplemental Privacy Statement for California Residents

California residents should read our Supplemental privacy statement for California residents in conjunction with this Privacy Notice. The Supplemental privacy statement for California residents explains Pearson's commitment to comply with California law and applies to personal information of California residents collected in connection with this site and the Services.

Sharing and Disclosure

Pearson may disclose personal information, as follows:

  • As required by law.
  • With the consent of the individual (or their parent, if the individual is a minor)
  • In response to a subpoena, court order or legal process, to the extent permitted or required by law
  • To protect the security and safety of individuals, data, assets and systems, consistent with applicable law
  • In connection the sale, joint venture or other transfer of some or all of its company or assets, subject to the provisions of this Privacy Notice
  • To investigate or address actual or suspected fraud or other illegal activities
  • To exercise its legal rights, including enforcement of the Terms of Use for this site or another contract
  • To affiliated Pearson companies and other companies and organizations who perform work for Pearson and are obligated to protect the privacy of personal information consistent with this Privacy Notice
  • To a school, organization, company or government agency, where Pearson collects or processes the personal information in a school setting or on behalf of such organization, company or government agency.

Links

This web site contains links to other sites. Please be aware that we are not responsible for the privacy practices of such other sites. We encourage our users to be aware when they leave our site and to read the privacy statements of each and every web site that collects Personal Information. This privacy statement applies solely to information collected by this web site.

Requests and Contact

Please contact us about this Privacy Notice or if you have any requests or questions relating to the privacy of your personal information.

Changes to this Privacy Notice

We may revise this Privacy Notice through an updated posting. We will identify the effective date of the revision in the posting. Often, updates are made to provide greater clarity or to comply with changes in regulatory requirements. If the updates involve material changes to the collection, protection, use or disclosure of Personal Information, Pearson will provide notice of the change through a conspicuous notice on this site or other appropriate way. Continued use of the site after the effective date of a posted revision evidences acceptance. Please contact us if you have questions or concerns about the Privacy Notice or any objection to any revisions.

Last Update: November 17, 2020